Potassium-sodium-lead alloy



Patented Aug.,-l3, 1940 UNITED STATES PATENT OFFICE POTASSIUM-SODIUM-LEAD ALLOY Harvey N. Gilbert, Niagara-Falls, N. 2., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application January 31,1939, Serial No. 253,862

'2' Claims.

' much more reactive toward air and moisture than metallic sodium. For this reason it is relatively hazardous to be shipped and handled. The metal may be prepared by reacting potassium compounds such as potassium hydroxide or potassium chloride with metallic sodium. Such methodsv of preparation usually produce the liquid alloy of sodium and potassium from which the two metals can be separated by distillation. The sodium-potassium alloy is even more reactive and hazardous to handle than pure potassium. A lead alloy containing a small amount of potassium is relatively unreactive and may be more safely -handled than pure potassium. However, the alkali metals, when added to lead, even in small amounts, form brittle alloys. The addition of small amounts of potassium to lead produces a very brittle alloy which has a low crushing strength and is very easily crushed or broken. Consequently, potassium-lead alloy containing suflicient potassium to make the alloy suitable as a source of potassium for chemical or metallurgical reactions has so little resistance to crushing and breaking effects that when handled or shipped, it tends to become broken into fine particles which are more reactive to air and moisture because of the large surface presented and for that reason it is somewhat hazardous to handle and also there is excessive loss of potassium by oxidation, unless expensive measures of protection are utilized.

An object of the present invention is to provide a form of potassium metal which is relatively resistant to oxidation and hydrolysis. A further object is to prepare a potassium alloy which is resistant to crushing and breaking and has high mechanical strength. My invention also includes a novel process for producing the aforesaid potassium-lead alloy. Other objects will be apparent from the following description of my invention.

The above objects may be attained in accordance with my invention by preparing a lead-potassium alloy which contains at least 83% by we ght of lead and a certain amount of sodium. The amount of sodium in this alloy is such that the weight ratio of potassium to sodium lies within the range of 0.4 to 7.5. Preferably the alloy contains about to 15% of potassium but the invention is not restricted to this range of potassium content.

I have discovered that by adding sodiumto a lead-potassium alloy, the brittleness of the alloy is decreased; the alloy is made tougher and its resistance to breaking and crushing by impact and crushing stresses is greatly increased. Lumps or molded pieces of the alloy may be transported and handled without precautions against breakage, and suffer substantially no mechanical damage or formation of any substantial amount of finely divided particles. At the same time, the addition of the sodium does not increase the reactivity of the alloy toward water and oxygen. As a result, the addition of sodium to the potassium-lead alloy produces an alloy of potassium which may be used for carrying out various reactions involving this element and which is safer and more advantageous to ship and handle than is pure potassium-lead alloy. I am unable to propose a. scientific explanation for these results obtained by adding sodium to potassium-lead alloy. As noted above, the addition of sodium to potassium to make sodium-potassium alloys produces a material which is more reactive to water and oxygen than either pure sodium or pure potassium. However, the sodium-potassiumlead alloy of the present invention is substantially not more reactive than a pure potassium-lead alloy of equal alkali metal content. Likewise, either sodium or potassium when added to lead hardens the latter, forming a brittle lead-alkali metal alloy. However, the addition of sodium to a potassium-lead alloy has a softening and toughening effect.

The composition of the herein described sodium-potassium-lead alloy may be varied as desired within the limits expressed above; 1. e., at least 83% by weight of lead and a weight ratio of potassium to sodium which lies within the range of 0.4 to 7.5 inclusive. I prefer, however, a potassium content in the alloy of about 5 to 15% by weight, a sodium content of at least 0.6% by weight, and a lead content of 83 to 90% by weight. For most purposes, the best results are obtained if the ratio of potassium to sodium in the alloy is in the neighborhood of 3:1. Thus a suitable alloy for most purposes may contain, for example, about 84% of lead, 12% by weight of potassium and 4% by weight of sodium. In making these alloys it is preferred, but not essential, that substantially pure lead be used, so that the lead alloys do not contain any substantial amount of a fourth constituent. Other metals, however, may be incorporated in the al- 10y if desired, provided that their presence is not incompatible with-the uses for which the potassium alloy is designed.

The potasslum-lead-sodium alloy of my in vention is of grey, metallic appearance. It is hard and tough, and pieces of it may be broken by hammering or crushing only with difliculty. When allowed to stand in the air, the alkali metal in the alloy slowly reacts to form a film of caustic and carbonate, but without appreciable formation of heat. When immersed in water, it reacts non-violently, slowly evolving hydrogen. Hence it may be used to generate hydrogen in conventional gas generating apparatus. It is preferable to store and ship the alloy in tightly closed containers to avoid excessive oxidation, but it may be safely handled and used in the air.

If desired, the aforementioned alloy may be prepared by any conventional method. Hovever, I have found that methods known heretofore for making potassium alloys are not well suited for the economical and efiicient preparation of my alloy and I have devised a novel method to this end. According to my novel method I react molten potassium hydroxide with molten metallic sodium in the presence of molten lead. Preferably I first prepare a molten alloy of lead and sodium, containing the required amount of sodium, and add molten potassium hydroxide. Preferably the molten hydroxide and the molten lead alloy are well stirred together for a sufficient time to permit the reaction between the sodium and potassium hydroxide to come to equilibrium. The resulting mixture of potassium and sodium hydroxides then may be removed, for example, by decantation and the resulting ternary alloy of potassium, sodium and lead may be molded into forms of suitable size.

In one method of carrying out my process I start with substantially anhydrous potassium hydroxide. If the anhydrous hydroxide is not available I may first dehydrate it by treating it in the molten state with a quantity of sodium which is chemically equivalent to the contained water. This results in a molten mixture of sodium hydroxide and potassium hydroxide, which mixture will have a melting point below that of potassium hydroxide. A suitable quantity of a sodiumlead alloy which may contain from 815% by weight of sodium is melted in a suitable vessel (which may be open to the air if desired) and the molten potassium hydroxide or potassium hydroxide-sodium hydroxide mixture is added so as to float on the surface of the sodium-lead alloy. The contents of the vessel then are vigorously agitated for about 30 minutes while the temperature is maintained at a temperature not lower than about 480 C., e. g., within the range 480 to 650 C. Best results are usually obtained by maintaining the temperature at about 500 to 550 C. After the reaction is completed, the molten hydroxide and the resulting ternary alloy may be separated by conventional means, for example, by decantation.

For efiicient and economical operation I prefer to carry out the reaction by passing the leadsodium alloy and the potassium hydroxide counter-current to each other in a suitable reaction apparatus. In one method of thus passing the molten lead alloy and the molten hydroxide counter-current to each other, I may carry out the reaction in four stages,'using four reaction vessels. Each reaction vessel is provided with a stirring device and suitable pumps of conventional design are provided for transferring molten hydroxide and the molten alloy from vessel to vessel. The sodium lead alloy is treated in the first vessel with molten hydroxide of lowest potassium hydroxide content and the alloy is suecessively treated in the next three vessels with molten hydroxide of successively increasing concentrations of potassium hydroxide until, in the fourth vessel, the alloy is reacted with substantially pure potassium hydroxide or with the hydroxide mixture obtained by dehydrating potassium hydroxide with sodium.

When the reaction is completed in the fourth vessel, the resulting supernatant mixture of sodium and potassium hydroxides is removed and reacted with alloy in the third vessel, and so on, so that the molten hydroxide progresses successively from the fourth to the first vessel. In this manner, the lead alloy having the highest sodium content is reacted with the molten hydroxide having the lowest potassium hydroxide content and the alloy having the lowest sodium content is reacted with the hydroxide having the highest potassium hydroxide concentration. The molten hydroxide removed from the first vessel is an anhydrous caustic mixture consisting mainly of sodium hydroxide with a minor amount of potassium hydroxide. This forms a valuable byproduct of the process. In this counter-current method, the number of reaction vessels may be varied as desired. By increasing the number of reaction vessels, the amount of potassium extracted from the molten hydroxide may be correspondingly increased.

Example A sodium-potassium-lead alloy containing 12% by weight of potassium and 4% by weight of sodium is prepared in four stages, using four reaction vessels, by the abo e described countercurrent method. A charge of 8077 lbs/of sodium lead alloy containing 11.6% by weight of sodium is placed in the first reaction vessel. Dehydrated hydroxide, prepared by treating 1839 lbs. of molten commercial potassium hydroxide with 160 lbs. of sodium, is charged into the fourth reaction vessel. The molten, dehydrated hydroxide contains 84.5% of potassium hydroxide and 15.5% sodium hydroxide. The spent caustic removed from the first reaction vessel consists of 1588 lbs. of a mixture of potassium and sodium hydroxides containing 14.8% of potassium hydroxide and containing in suspension about 156 lbs. of lead alloy. The alloy removed from the fourth vessel (8320 lbs.) contains 12% of potassium, 4% of sodium and 84% of lead. The following table shows the compositions of the lead alloys and the hydroxides charged into and removed from each reaction vessel during each complete cycle of operation:

Reaction vessel 1 2 3 4 Allo char ed 88.4 Pb 87.2 Pb 85.4 Pb. y g 7 5.84% Na. 8.76% K. Alloy removed 84.0% Pb.

4.0% Na. 12.0% K.

Hydroxide charged 35.4% KOH 53.7% KOH 69.8% KOH 84.5% KOH.

64.6% NaOH 46.3% NaOH 30.2% NaOH 15.5% NaOH.

Hydroxide removed 14.8% KOH 35.4% KOH. 53.7% KOH 69.8% KOH.

85.2% NaOH 64.6% NaOH 46.3% NaOH 30.2% NaOH.

In carrying out the process illustrated by the above example, the four reaction vessels advantageously may be arranged close together in a single furnace setting.' The molten hydroxide and alloy may be pumped from vessel to vessel by means of a conventional pump adapted for the purpose. The fourth vessel preferably is equipped with a bottom outlet, by means of which the finished alloy may be drawn off into molds.

In an alternative method of using a series of reaction vessels for thecounter-current reaction, I may flow only one of the reactants, e. g., the molten hydroxide, from vessel to vessel. In this way, the final operation to produce the finished alloy will occur successively in different vessels. Y

The above methods for counter-currently reacting the sodium lead alloy and the potassium hydroxide may be varied considerably without departing from the essential conditions of my process. Thus the number of the reaction vessels or stages may be more or less than four although for reasons of convenience and economy I found four to be preferable. Also the same process may be carried out in a single reaction vessel but it is preferable to use a plurality of them.

In still another method of carrying out the reaction counter-currently, I may maintain a body 'of molten potassium hydroxide in a high tower-like container with or without plates or packing materials therein and cause a slow stream or streams of molten sodium lead alloy to flow therethrough, for example, by flowing the sodium lead alloy through the bottom of a perforated pan located at the top of the tower. In my preferred method of carrying out the reaction in such a tower, the moltenpotassium hydroxide is forced in at the bottom of the tower and floated off at the top. The resulting ternary alloy collecting in the bottom of the tower may be drawn off continuously or intermittently.

The concentration of the sodium in the sodium lead alloy may be varied over a wide range depending upon the desired sodium content in the final product, the initial strength of the potassium hydroxide-sodium hydroxide mixture and the specific conditions of the method used.

I claim:

1. A homogeneous alloy of lead, potassium and sodium which is highly resistant to crushing and breaking, and which reacts non-violently with water, containing not less than 83% by weight of lead, and in which the weight ratio of potassium to sodium is about 3.0 to 1.

3. A homogeneous alloy of lead, potassium and sodium which is highly resistant to crushing and breaking, and which reacts non-violently with water, containing about 83 to 90% by weight of lead, and in which the weight ratio of potassium to sodium is about 3 to 1.

4. A homogeneous alloy of lead, potassium and sodium which is highly resistant to crushing and breaking and which reacts non-violently with water, containing not less than 83% by weight of lead, from 5 to by weight of potassium and a quantity of sodium such that the weight ratio of potassium to sodium lies within the range of 0.421 to 75:1.

5. A homogeneous alloy of lead, potassium and sodium which is highly resistant to crushing and breaking and which reacts non-violently with water, containing approximately: 84% by weight of lead, 12% by weight of potassium and 4% by weight of sodium.

6. The process which comprises reacting commercial potassium hydroxide containing water in the molten state with sodium to produce a substantially anhydrous mixture of sodium and potassium hydroxides and reacting said mixture with sodium in the presence of lead, at a temperature not lower than about 480 C., to produce an alloy of potassium, sodium and lead.

'7. A homogeneous alloy of lead, potassium and sodium containing 83 to 90% by weight of lead, in which the weight ratio of potassium to sodium lies within the range of 0.4:1 to 7.5:1.

HARVEY N. GILBERT. 

